1. Field of the Invention
This invention relates generally to the field of power supplies, and, in particular, to standby mode power supplies for video display apparatus such as, for example, television receivers.
2. Background Information
The power consumption of a video display apparatus may approach, or even exceed, approximately ten watts during standby mode operation. At a time of heightened governmental concern regarding energy efficiency standards for electronic equipment, such a level of standby power consumption poses a concern. For example, an article in the Sep. 19, 1997, issue of Europe Energy reports that the European Commission regards reducing the energy consumed by electronic equipment in the standby mode of operation as a priority. The article further states that the Commission has concentrated its initial efforts at reducing the standby power consumption of televisions and VCRs, and that it has elicited voluntary commitments from manufacturers of such products to progressively reduce average standby power consumption to less than three watts.
A conventional power supply arrangement for a video display apparatus is disclosed in Japanese laid-open patent document number JP 6-225529. A run mode output stage 2 is coupled to a converter 1 through a switch SW, and a standby mode output stage 3 is inseparably connected to the converter 1. The arrangement disclosed in JP 6-225529 is undesirably inefficient because the standby mode output stage 3 dissipates power during the run mode of operation.
In another conventional power supply arrangement for a video display apparatus, a single power supply circuit is used to implement both standby and run mode operation. When the power supply control circuit senses that the secondary side of the power supply is unloaded, the power supply is placed into a "burst" mode of standby operation, whereby the power supply continues to generate standby voltages for the remote control receiver and the microcontroller.
A disadvantage of this conventional power supply implementation is that the primary inductance of the switched mode power supply transformer is too low for proper standby operation. This low primary inductance results in increased power consumption by the video display apparatus in the standby mode. The reduction in the energy consumed by the video display apparatus during the standby mode of operation dictates either that the pulse width of the drive pulses from power supply control circuit be reduced; or, that the inductance seen by the drive pulses during the standby mode be increased relative to the inductance of the primary winding of the switched mode power supply transformer.
Because of the constraints imposed on the pulse width by the power supply control circuit, it is desirable to increase the inductance seen by the drive pulses during the standby mode, in order to reduce the power consumption of the video display apparatus during the standby mode of operation, preferably to a level equal to or below one watt.